I'm not sure what your argument is. Sophisticated investors don't invest in obvious scams. That's tautologically true. Does that mean we should just watch and do nothing while people get scammed?
The thing is, nobody is born sophisticated and there are many ways to get hurt in financial markets in the absence of scams even if you're intelligent and do your homework.
You mention index trackers, but they are no silver bullet. Their mechanism is basically to buy more of stocks that go up, and to sell those stocks that stumble badly. The more people rely on index trackers (exchange traded or not) the more volatile they'll become, and because index funds use such a simple trading strategy it's easy to front-run or otherwise exploit them. Furthermore, index trackers depend on active investors for price discovery, and the fewer active investors you have the worse index funds will perform. Relying on a vanguard ETF might continue to work, but to assume that it will is hopelessly naïve. It's no coincidence that ETFs got so popular with interest rates at 0 and a fed that made stonks go up.